1. Field of the Invention
The invention relates to an arrangement and a method for controlling the speed of an internal combustion engine in an implement.
2. Description of the Related Art
Implements of this type, for example a vibrating rammer for soil compaction or a strike hammer, have a gasoline engine, but sometimes also a diesel engine, for the drive. The engine isxe2x80x94if an electric starter is not providedxe2x80x94usually started by actuation of the pull cable of a reversible starter. To this end, the operator firmly holds the rammer, for example, with one hand while he pulls on the pull cable with the other hand. Since the throttle lever of the engine is generally set to a full-throttle setting for the start, the engine immediately operates at a high speed which often even lies above the operating speed. This closes a centrifugal clutch which connects the engine to the ramming system, as a result of which the ramming system is put into operation. This leads to the rammer executing powerful ramming movements and the operator, who is only holding the rammer at this point with one hand, is scarcely able to control it. The ability to control it is also made more difficult by the rammer being set at a slight angle at the start so as to more easily reach the pull cable. The ramming movement does not therefore take place exclusively in the vertical direction, but also to the side, which also makes it more difficult to operate and the operator is even put at risk. Similar problems may also arise in the case of vibrating plates.
In addition, during starting a choke flap on the carburetor is generally closed and has to be opened again at the end of the starting operation. The overly rich combustion mixture directly after the starting causes the engine to operate irregularly, resulting in irregular, uncontrolled movements of the rammer. While this is happening, the operator has to attempt to reach and operate the choke lever, which is arranged on the carburetor below the operating elements, which means that he has to risk going near the erratic rammer with his head and arm. This activity is also made more difficult by it being necessary to grasp, i.e. not let go of the rammer""s holding loop.
A device for limiting the speed of an internal combustion engine to a maximum permissible governed speed is described in DE 196 09 536 A1. The exceeding of the governed speed is detected by a sensor which activates, via electronics, a gear motor which overrides a throttle-lever setting and by means of which the setting of a throttle of the internal combustion engine can be influenced.
EP-A-242 809 has disclosed a vibrating plate which can be guided in a handle. Provided below the handle is an additional deadman""s handle which is connected to a throttle cable. In order to bring the engine of the vibrating plate up to an operating speed, it is necessary for the operator to pivot the deadman""s handle upward and to hold it against the operating handle. As soon as the operator lets go of the deadman""s handle, the latter pivots downward because of its dead weight and reduces the engine speed to an idling speed via the throttle cable.
The invention is based on the object of specifying an arrangement and a method for an implement, in which uncontrolled initial operation of the implement and the more difficult handling which is associated therewith during starting, but also in the case of other special operating states, for example which put the operator at risk, are avoided.
According to the invention, the object is achieved by an arrangement in accordance with patent claim 1 and by a method in accordance with patent claim 8. Advantageous further developments of the invention are revealed in the dependent claims.
The invention specifies an arrangement for controlling the speed of an internal combustion engine in an implement, having a recognition device for recognizing a special operating state of the implement brought about by action from outside the implement, and having an adjusting device, which can be activated by the recognition device, for adjusting the engine speed to a safety speed below an operating speed of the internal combustion engine.
The recognition device makes it possible to register a special operating state of the implement, for example the starting of the implement, but also hazardous states due to letting go of holding handles of the implement or due to the implement tipping over, whereupon a corresponding signal is delivered to the adjusting device which reduces the engine speed to a perceptibly lower, and therefore nonhazardous speed, for example the idling speed. Only if the recognition device no longer recognizes a special operating state is it possible again for the operator to increase the speed.
At the special operating state, a state is advantageously recognized in which the implement is started or is not guided correctly or an angular setting of the implement which is outside a permissible range is recognized.
In order to recognize the starting operation, it is possible for the recognition device to register a rise in speed of the internal combustion engine from standstill. Furthermore, in a particularly advantageous embodiment of the invention, the recognition device can ascertain if the ignition system of the internal combustion engine is supplied with power, which is likewise interpreted as a starting operation. This embodiment is suitable in particular for internal combustion engines having a magneto ignition system, in which the ignition power is not provided by an external power source, but is produced directly by a magnetic wheel revolving on the engine shaft. The presence of ignition power is then equivalent to the exceeding of a certain engine speed.
As an alternative to this, it is also possible to find solutions for every other type of ignition system which enable the starting operation and/or the rise in speed to be recognized. In the case of battery ignitions it is possible, for example, to pass on a signal, which is taken from the crankshaft and corresponds to the speed of the crankshaft, to the recognition device.
In another advantageous embodiment of the invention the recognition device has a timing element by means of which a predetermined period of time after starting of the engine is monitored and during which the engine speed is adjusted to a safety speed. Only after the predetermined period of time has elapsed is it possible for the adjusting device to increase to operating speed, it being assumed that after the period of time has elapsed, the engine operates regularly and the operator has in the meantime gained control over the rammer or over the implement.
A particularly advantageous further development of the invention is defined by the recognition device having at least one switching or sensing unit. A switching or sensing unit of this type may be a safety loop or handle which can be held by the operator. Also conceivable are corresponding sensors on the holding handle, the sensors being used to register the fact that the operator is holding the holding handle of the implement correctly. only in this case does the recognition device recognize a normal operating state enabling running at the operating speed.
In another further development of the invention the recognition device has a device for determining the position of the implement, in particular the angular position, and, when a predetermined position limit is exceeded, recognizes a special operating state.
This makes it possible, for example when the implement turns over, to immediately adjust the internal combustion engine to a safety speed and to avoid putting the operator at risk.
A method according to the invention for controlling the speed of an internal combustion engine in an implement has the following steps:
recognition of a special operating state of the implement, and
if a special operating state has been recognized, adjusting the engine speed to a safety speed below an operating speed of the internal combustion engine.
Both the arrangement and the method can be used particularly advantageously in the case of a rammer or a strike hammer having an internal combustion engine.
These and further advantages and features of the invention are explained in greater detail below with reference to preferred embodiments.